Last year I came across a design from Markus Bernhardt, www.baer-bel.de that I liked but he didn't want to make anymore.
I recently discovered www.shapeways.com , a 3-D printing service.
I designed rings based on Markus Bernhardt's design with Google SketchUp, converted it in Meshlab and then opened it in Netfabb to finalize size and output a .stl file to upload.
These are all free software that can be downloaded.
Mine is here http://www.shapeways...ing.html?gid=mg
This is for the early Bartech that had a slightly different knob diameter
I have 20 rings and there are small variations as some are tighter but all fit.
I recommend you order one (wether my design or yours) to test before you order a large number. I am not selling them(I'm not adding a markup), you are ordering from Shapeways.
The price with customs is about $20 a ring.
If someone designs one for the new diameter or a different design please post it.
You should be able to download the design. If it's not working I can send you my file.
"Opensource Focus rings"